The objectives of this study are threefold: (1) to use thermoregulatory responses of the cat to evaluate the hypothesis that narcotic agents act on three distinct types of opiate receptor, (2) to determine the functional components of the thermoregulatory system primarily affected (a) by stimulation of each type of receptor and (b) by precipitation of abstinence in dependent animals and (3) to determine chemical mediators of responses to stimulation of these receptors and also their anatomical locations within the thermoregulatory system. The results will be compared with effects produced by administration of endogenous opioid peptides or their analogues, such as beta-endorphin and D-ala2-methionine-enkephalin, to determine if these peptides stimulate a specific type of receptor within the thermoregulatory system. Techniques will include (1) automatic recording of body temperature in unanesthetized, unrestrained cats, (2) drug injections via a variety of routes including intracerebroventricular, intravenous and directly into cerebral tissue, all via chronically implanted cannulas, catheters and guide tubes, (3) visual observation for evidence of changes in physiological and behavioral thermoregulatory activities following drug injection, (4) determination of drug effects on body temperature at a variety of environmental temperatures and (5) heat-reinforcement or heat-escape behavior in trained animals. Whenever possible, cross-over studies will be done in which each of the animals receives each of the possible treatments including control injections of equal volumes of vehicle in randomly determined order.